How Apple’s Secretive Gym Is Shaping Its Activity-Tracking Algorithms

The fitness lab for the Apple Watch includes dozens of metabolic carts, a fleet of full-time nurses, and an endless pool.

Starting in the fall, the Apple Watch will be able to communicate with gym equipment to track your workouts, as this image from the company shows. To build the algorithms behind this activity tracking, Apple has a secretive AI gym where it gathers data from employee testers.

For several years now, Apple has operated a hush-hush fitness lab in an undisclosed location at its campus in Cupertino, California, and this week the company offered up a few details about how it’s studying all kinds of activities—on dry land and in water—in order to build algorithms for tracking them on the Apple Watch.

Jay Blahnik, Apple’s director of fitness for health technologies, said Tuesday that Apple believes the gym-like lab—which was built before the Apple Watch was released in 2015 and uses employee volunteers as guinea pigs—has now collected more biometric data than anyone else. It has also become the largest purchaser of metabolic carts, which are used to keep tabs on oxygen consumption; it now has 50 of these machines, he said, and half of them are portable so they can be used for activities like swimming and cycling. (And employees do use them, along with a security guard, for a daily bike ride, he added.)

The swimming happens in an indoor endless pool, and Blahnik said observations revealed that people don’t swim as well as they think they do. It turns out that even when people are pretty regular swimmers, it’s hard to measure a difference between, say, their crawl and breaststroke.

That’s not to say that everyone who comes into this data gym is going to partake in physical activity.

“One day you might show up and we’ll study how many calories you burn while you sit, because we need to understand that, too,” he said.

Blahnik spoke about Apple’s AI gym during a series of demos the company showed off to a small group of reporters in Los Angeles on Tuesday. The demos, presented by Apple itself and several outside developers, showed the Apple Watch’s newest and upcoming health and fitness capabilities—including a feature that wirelessly links the watch directly with a treadmill to track your workout, which will be available in the fall with the release of the new Apple Watch OS, WatchOS 4, and compatible gym equipment.